1. Field of the Invention
The invention relates to a chemical flow management (CFM) full flow processor chemical inject control aspiration system and a method of using same to inject a fluid additive into a primary carrier liquid.
2. Description of the Related Art
In the fabrication of integrated circuitry on a semiconductor wafer, it is imperative to maintain the purity and perfection of the material. For example, semiconductor wafers are routinely chemically cleaned after many processing steps to remove any unwanted organic films, heavy metals, particulates, and debris from the surface of the wafer. Also, wet etchants are often used in the removal of bulk material from a wafer surface, such as an etchant component of a slurry used in surface polishing operations or for local etching in fabrication steps used to delineate surface features. The cleaning and etching solutions used for these purposes usually are aqueous mixtures formed by dilution of a chemical reagent or concentrate, or a combination of such, in a dilutant. In semiconductor processing, the dilutant of choice is deionized water. The performance and aggressiveness of the cleaning solution can be a strong function of the dilution rate of active chemical(s). Due to the fineness of microcircuitry, any inadvertent fluctuations in the mixing ratios of the chemical reagents with water can adversely impact and frustrate efforts at quality control. Therefore, consistent and reliable control of the mixing procedure used in preparing the cleaning and etching solutions used in IC chip fabrication is very important and highly desired.
A conventional CFM tool used in semiconductor applications generally prepares process solutions by injecting or entraining chemical concentrates or other chemical reagents into a stream of continuously flowing deionized water. Semiconductor processing wet tools have used mechanical devices in combination with a pneumatic chemical injection system to control the flow rate of required chemical additives into the processing chamber of the wet tool when called for by the process program. In the conventional systems, the water pressure is adjusted to adjust the amount of chemical injection and, consequently, the chemical injection is inversely proportional to the water pressure/flow.
A conventional CFM tool 10 is illustrated in FIG. 1. An injection tube cylinder 11 is filled with the chemical reagent or additive, and the additive is pressurized at the proper time using dome-loaded regulator 14. The opening of a needle valve 12 is manually adjusted initially to provide a predetermined volume of wet chemical reagent via feed line 16 at a specified pneumatic pressure over a finite period of time. The additive(s) is supplied then flows through manually-adjusted needle valve 12 and mixes with the dilution water supplied via carrier liquid source stream 15 in a sampling valve 13. A sampling valve is a standard piping component with a large bore and which is constantly open, and a small side tap which is isolated by a normally closed valve. This allows a small amount of the stream flowing through it to be sampled, or conversely a small amount of an additive to be injected into the main flowing stream. A standard 0.25 inch (0.64 mm) PFA adjustable needle valve installed in a manifold has been used as needle valve 12. To achieve a range of flow requirements, the pneumatic pressure is adjusted correspondingly. Namely, the mixing ratio is controlled by adjusting the cylinder pressurization in the injection tube 11 by use of the dome loaded regulator 14, which acts against a resistance controlled by adjustment of the needle valve 12 and the head pressure of the water at the sampling valve 13. The mixture of additive and dilutant water is conducted to wafer processor 17 for usage.
This conventional CFM system allows a dynamic range in the mixing ratio of 2.5.times. (e.g., the system can supply chemicals at a ratio of 100:1 to 250:1). This mixing ratio is bounded by the pressure ratings of the components in the injection tube 11 assembly at its upper limit and by the static pressure of the water the system is injecting against. The timing, pressure and valve adjustments all must be controlled in a coordinated manner to give an accurate injection of the chemical in this conventional system. Also, the static pressure of the deionized water at the injection point is well above atmospheric pressure in this conventional system. This property tends to restrict the dynamic range possible in the mixing ratio of water and injectate for the injection system. In this regard, it will be appreciated that in any flow system, the fluid exerts two pressures on its surroundings. One being the dynamic pressure exerted against a surface perpendicular to the direction of flow, and the other being a static pressure exerted against a surface, such as a pipe wall, oriented parallel to the direction of flow. At the point of injection, the injectate is being injected through a hole in the pipe wall; hence, the injectate is injected against the static pressure of the flowing deionized water.
Furthermore, the conventional flow mixing system has been unstable with respect to the ratio of the flow rate of the injected additive (and consequently the chemical concentration in the processing solution). In this conventional system depicted in FIG. 1, the mixing process was based on changing pressure to adjust the amount of chemical injection, and, therefore, the chemical injection was inversely proportional to the water pressure/flow. At any time, the instantaneous rate of flow of the additive (injectate) would be proportional to the pressure difference between the pressure applied to the injection tube 11, which is a fixed pressure, and the head pressure of the water at the mixing point within sampling valve 13. A transient increase in the water flow rate would cause an increase in this pressure. As the injection pressure of the additive is fixed, the change in P (.DELTA.P) for the additive suffers a decrease, resulting in a proportional decrease in the additive flow. As a consequence, any transient change in the water flow rate would undesirably induce the opposite effect in the additive flow rate.
The impact of this effect is magnified by the way in which the CFM tool is typically used. Namely, the most critical and sensitive cleaning and etching operations are carried out at high dilution ratios of the etchant chemical in the carrier fluid. In order to preserve the dynamic range of the CFM tool under these circumstances, the needle valve 12 is adjusted so that these injections take place at low pressure. However, as the error in flow is proportional to the ratio of the transient pressure excursion to the desired .DELTA.P for the injected additive, the relative error in flow for a given pressure excursion is magnified under these conditions. As a consequence, the adjustment and control of these mechanical devices and pneumatic injection systems is very complicated and often inaccurate, especially at lower chemical flow volumes.